Chimps creep closer yet.

Chimpanzees may be more closely related to humans than to any other primate, new genetic evidence suggests.

"We all know that humans and chimps are extremely close genetically," says study coauthor Soojin Yi, an evolutionary biologist at the Georgia Institute of Technology in Atlanta. The two species diverged from a common ancestor from 5 million to 7 million years ago and have 95 to 98 percent of their DNA in common, previous research has established.

But by measuring the accumulation of small differences in DNA between the two species, Yi and her colleagues found another shared trait: a slow "molecular clock," or rate of evolutionary change.

Of all primates, modern people live longest, have the longest gestation time, and reach sexual maturity latest, Yi says. More time between generations means slower rates of evolution at the level of DNA, or a slower molecular clock, she says.

But chimp clocks don't tick much faster, the new study shows. After analyzing millions of base pairs of DNA in people and other primates, including chimps, baboons, and gorillas, the researchers found that while the human clock is 3 percent slower than the chimp's, it is 11 percent slower than the gorilla's. Taking into account the small difference between human and chimp clocks, the team calculated that people's longer time between generations and large brains evolved only 1 million years ago. The findings appear in the Jan. 31 Proceedings of the National Academy of Sciences.

The new finding bolsters a controversial idea that people and chimps share a genus, Yi says.

The study is "exceptionally interesting," says molecular evolutionist Morris Goodman of Wayne State University in Detroit. "We humans have an exaggerated opinion of how great we are."--C.G.